Lesson 7 - Mashing Technology SAQ
This lesson provides the opportunity for you to test yourself on the material covered in Lesson 6 on Mashing Technology and determine the level to which you have attained the expected outcomes.
SAQ Suggested Response - Q2
**Describe how mashing technology at each stage of the mashing process is designed to minimise shear forces on the mash.
Response:
The best approach to this question is to take it one activity at a time. We can start at the beginning with pre-mashing.
Pre-mashing
In-line pre-mashers cause the most shear of the options available, but we can reduce this to a degree by directing the mash leaving the pre-masher onto the wall of the vessel. Adding foundation water to the mashing vessel to cushion the landing of the mash in the bottom also helps. Pumping the mash at low speed into the base of the vessel is the approach that produces the lowest shear.
Agitation
The shape of the agitator affects the amount of shear caused. Agitators should be angled, so they gently push mash, and large differences in pressure and velocity in the mash are not created as they move. The speed of the agitator is also critical. Tip speed should be as low as possible without compromising mixing. < 1 m/s has been suggested as a target, but typical tip speeds used are < 3 m/s.
Mash transfer
The slower the movement, the lower the shear, so the pipes carrying the mash need to be sized so the pump can move the mash at less than 1.5 m/s. Bends and obstructions (fittings, valves, probes, unions) should be minimised as each can cause velocity changes and hence increase shear. Any bends that cannot be eliminated from the design should be long and sweeping to ensure velocities and pressures are even along the pipe. Low pump speeds also reduce shear, so the pump should operate at < 1,000 rpm. Most importantly, the pump should be on the correct point on its design curve throughout transfer.